**Abstract**

Type 2 diabetes mellitus accounts for ≈90–95% of those with diabetes, about 50% of those with type 2 diabetes are unaware and it can remain undiagnosed for up to 12 years, ≥25% of people have evidence of microvascular complications at diagnosis. The consequences of diabetes can be reduced by screening and early interventions. Urinalysis as a screening test is limited by its low sensitivity ranging from 21% and 64%, though has high specificity (>98%), it has a place where no other procedure is available. Fasting plasma glucose though recommended as a universal screening and diagnostic test for diabetes mellitus, a changed in the diagnostic criteria was made when this did not give corresponding hyperglycaemic impact compared to the OGTT results, bringing a complex and variable effect on the prevalence of diabetes and on subjects diagnosed. To date the searching to finding the corresponding FPG to what is normal or IGT is still ongoing. FPG testing poorly identify early signs of dysglycaemia. This is due to the difficulty ensuring compliance with instructions about fasting, FPG represents glucose handling during the moment of fasting period only and is affected easily by short-term lifestyle changes, FPG has diurnal variation, higher in the morning than in the afternoon, these may cause serious misclassifications. OGTT do indicates the pathophysiology responsible for diabetes better as it provides information on what happens in the postprandial state when the functional capacity of pancreatic β-cell is crucial. It accurately detects changes in post-prandial glycaemia that tend to precede changes in fasting glucose. OGTT is the gold standard for the diagnosis of GDM and the only means of identifying people with IGT and WHO placed emphasis on the OGTT as the "gold standard", in diagnosis of dysglycaemia. Reproducibility can be improved remarkably when patient preparation, a forvarable atmosphere during the procedure, standardized sampling protocol, sample handling, and analysis are given high attention. Measurement of A1c equals the assessment of hundreds of FPG levels and also captures postprandial glucose peaks. Regrettably, it has been shown that 44% of people with newly diagnosed diabetes with OGTT had A1c <6.0% and that a stronger correlations with plasma glucose is better in subjects with known diabetes, but not in the general population. A1C values just above the upper limits of normal require OGTT to be correctly interpreted; it is not available in many part of the world. Finally, A1c can not diagnose IFG and IGT to disclose high-risk subjects for

diabetes. In conclusion an OGTT is undeniably the best test in investigation of dysglycaemia, either with the intention of testing for pre-diabetes, type 2 diabetes, or for gestational diabetes mellitus.

from 1 to 14% of pregnancies, depending on the population studied. GDM represents nearly 90% of all pregnancies complicated by diabetes. Deterioration of glucose tolerance occurs normally during pregnancy, particularly in the 3rd trimester.

*Oral Glucose Tolerance Test (OGTT): Undeniably the First Choice Investigation…*

a. **Genetic defects of the β-cell:** Fair numbers of diabetes are affiliated with monogenetic defect in β-cell function, referred to maturity onset diabetes of the young (MODY) and are characterised by impaired insulin secretion with minimal or no defects in insulin action. Inherited in an autosomal dominant

b. **Genetic defects in insulin action:** These are rare causes of diabetes sequel to genetic abnormalities of insulin action. The metabolic flaws amalgamated with mutations of the insulin receptor may traverse from hyperinsulinaemia and modest hyperglycaemia to severe diabetes and some may have acanthosis

nigricans, women may be virilized and have enlarged, cystic ovaries. Leprechaunism and Rabson-Mendenhall syndromes are two paediatric

c. **Diseases of the exocrine pancreas:** Any process that diffusely injures the panaceas can causes diabetes, ranging from infections, trauma, metabolic,

d. **Endocrinopathies:** Several hormones (growth hormone, cortisol, glucagon, epinephrine) antagonize insulin action. Excess amounts of these hormones as

f. **Infections:** Certain viruses have been associated with β-cell destruction; eg. Congenital rubella, Coxsackievirus B, cytomegalovirus, adenovirus, and mumps have been implicated in inducing certain cases of the diabetes

h. **Other genetic syndromes sometimes associated with diabetes:** Many genetic syndromes are accompanied by an increased incidence of diabetes mellitus, eg., Down's syndrome, Klinefelter's syndrome, and Turner's syndrome. Wolfram's syndrome is an autosomal recessive disorder characterised by insulin-deficient

Diabetes burden goes beyond individual but extends to families and society as a whole. It has huge consequences affecting both national productivity and economies particularly in the low- and middle-income countries when considering the

e. **Drugs or chemical-induced diabetes**: Many drugs can impair insulin secretion. These drugs may not cause diabetes by themselves but they may

g. **Unknown forms of immune-mediated diabetes:** In this variety, two conditions are known, others may occur. The stiff-man syndrome distinguished by inflexible axial muscles with painful spasms. Patients routinely present with high titers of the GAD autoantibodies, and roughly

syndrome with mutations in the insulin receptor gene

noted in acromegaly, Cushing's syndrome, glucagonoma, Phaeochromocytoma, respectively can cause diabetes

precipitate diabetes in individuals with insulin resistance

**Other specific types of diabetes** [4]**:**

*DOI: http://dx.doi.org/10.5772/intechopen.96549*

pattern

and rarely neoplasm

one-third will develop diabetes

projection for the year 2025.

**113**

diabetes and the absence of β-cells at autopsy

**Prevalence and burden of diabetes mellitus, Table 1.**

**Keywords:** Dysglycaemia, T2DM, GDM, Screening, Urinalysis, Fasting Plasma Glucose, OGTT, A1c
